Answer
(C) $5.40\times 10^{-7}N$
Work Step by Step
We can find the magnitude of electrostatic force as follows:
$F=\frac{Kq_1q_2}{r^2}$
We plug in the known values to obtain:
$F=\frac{(8.99\times 10^9)(93.0\times 10^{-12})^2}{(0.0120)^2}$
$F=5.40\times 10^{-7}N$